why do fish have scales?

Answer 1

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Do all fishes have scales?
No. Many species of fishes lack scales. All the clingfishes (family Gobiesocidae) for example, are scaleless. Their bodies are protected by a thick layer of mucous.

Why do fish have scales?
The primary purpose of scales is to give the fish external protection.

How many types of scales are there?
There are four main kinds of scales and numerous variations of each kind.

Placoid
Cosmoid
Ganoid
Cycloid and Ctenoid
Different fishes, different scalation
It is interesting to think about the lifestyle and habitat of a fish, then look at its scales. In the Shark Scale Brain Teaser, the scales of five shark species are shown, two are slow swimming bottom-dwelling sharks, one is a generalist predator, and two are fast swimming pelagic species. Can you work out which scale belongs to each shark?

Are all scales the same size?
No. Scale sizes vary greatly between species. Some fishes, such as the freshwater eels have tiny embedded scales. Fishes such as the tunas have tiny scales often found in discrete areas of the body. Many fishes such as the Coral Snappers have medium sized scales whereas the scales of others such as the Tarpon, Megalops cyprinoides are large enough to be used in jewelery. The scales of the Indian Mahseer, Tor tor are known to reach over 10 cm in length.

How old is a fish scale?
As cycloid and ctenoid scales increase in size, growth rings called circuli become visible. These rings look a little like the growth rings in the trunk of a tree. During the cooler months of the year the scale grows more slowly and the circuli are closer together leaving a band called an annulus. By counting the annuli it is possible estimate the age of the fish. This technique is extensively used by fisheries biologists.

Can a fish have more than one type of scale?
Yes. Some species of flatfishes (flounders, soles, etc) have ctenoid scales on the eyed side of the body and cycloid scales on the blind side.

Answer 2

According to ichthyologists, scales are like a suit of armour that protects a fish, yet allows flexibility so it can move. Scales, like trees, have growth rings, and can help scientists tell how old a fish is. The scales are replaceable if they are damaged, and are sensitive, as skin is, to the surroundings, so when fish try to swim through a narrow channel, they don't get stuck.
They also allow the water to flow smoothly and freely over them, so the fish can swim efficiently.

Answer 3

Their bodies are protected by a thick layer of mucous. The primary purpose of scales is to give the fish external protection

Answer 4

Maybe so it is tough for an enemy (predator, like us! Ha! twice) to hang-onto them as in "survival of the fittest."
That slime...you know?

Answer 5

for protection and to maintain body temperature

Answer 6

external protection.

Answer 7

to protect themselves.

Answer 8

Cause that's how God made them!

Answer 9

so they can weigh themselves